When the Lights Go Out

You may have no warning. But usually you feel nauseated or lightheaded, become sweaty and pale, then experience a graying out of your vision.

Within about a minute of lying flat, sufficient blood flow to your brain is restored and you regain consciousness.

A Symptom With Many Causes

About 25 percent of adults faint because of a heart condition. In as many as 35 percent of people, the reason is unknown.

In other cases, fainting may be due to a drop in blood pressure related to these factors:

Standing too quickly

When you stand, your sympathetic nervous system triggers release of the hormone adrenaline. This leads to an increase in your heart rate and blood pressure, preserving adequate blood flow to your brain.

With age, this cardiovascular response can slow. Standing too quickly may cause blood to pool in your legs, leading to a sudden drop in blood pressure.

Medications

High blood pressure drugs and antiarrhythmics that slow heart rate are typically associated with fainting.

These drugs can make you more susceptible to blood pressure changes. They also can keep your heart from beating fast enough to meet higher demands caused by a change in position or activity.

Activity

Adequate sodium helps maintain blood pressure. Sodium lost through excessive sweat during strenuous activity, especially in heat and humidity, can lead to a drop in blood pressure.

Ways to Prevent Fainting

A few simple steps may keep you from fainting:

Lower your head

If you feel as though you're going to faint, lie down. Raise your legs above the level of your head to increase blood flow to your brain.

If you can't lie down, sit or bend forward with your head between your knees. Wait until the lightheadedness or nausea has subsided before trying to stand.

Stand slowly

This gives your blood pressure and heart rate more time to adjust to an upright position.

Check medications

If a new drug or change in prescription causes occasional lightheadedness, talk with your doctor. You may need an adjustment in your dosage.

If you take several medications, don't take them all at the same time unless your doctor advises otherwise. The combined effect may overwhelm your body's ability to maintain homeostasis.

Pace yourself

When working or exercising in heat and humidity, take frequent breaks and drink plenty of liquids.

Don't Minimize Fainting

If you have a chronic health condition such as cardiovascular disease, high blood pressure or diabetes coupled with recurrent fainting, have your doctor evaluate the problem. Contact your doctor about even a single fainting episode if you're more than 40 years old.

When Fainting Indicates Something Dangerous

Critical causes of fainting usually mean complications with the heart or the blood vessels going to your brain. The most frequent heart condition is an abnormal rhythm, it decreases the amount of blood pumped from your heart.

Acute shrinking of the aortic valve (aortic stenosis) or build up of plaque in the carotid arteries may be the reason for fainting by restricting blood flow going to the brain.

Consult your doctor immediately if fainting happens without warning, when you turn your head or extend your neck, or when accompanied by shortness of breath, blurred vision, irregular heartbeat, trouble talking, confusion or chest pain.